Narrow-band Vibration Research Articles

Onset and nature of flow-induced vibrations in cerebral aneurysms via fluid–structure interaction simulations

Clinical, experimental, and recent computational studies have demonstrated the presence of wall vibrations in cerebral aneurysms, thought to be induced by blood flow instability. These vibrations could induce irregular, high-rate deformation of the aneurysm wall, and potentially disrupt regular cell behavior and promote deleterious wall remodeling. In order to elucidate, for the first time, the onset and nature of such flow-induced vibrations, in this study we imposed a linearly increasing flow rate on high-fidelity fluid–structure interaction models of three anatomically realistic aneurysm geometries. Prominent narrow-band vibrations in the range of 100–500 Hz were found in two out of the three aneurysm geometries tested, while the case that did not exhibit flow instability did not vibrate. Aneurysm vibrations consisted mostly of fundamental modes of the entire aneurysm sac, with the vibrations exhibiting more frequency content at higher frequencies than the flow instabilities driving those vibrations. The largest vibrations occurred in the case which exhibited strongly banded fluid frequency content, and the vibration amplitude was highest when the strongest fluid frequency band was an integer multiple of one of the natural frequencies of the aneurysm sac. Lower levels of vibration occurred in the case which exhibited turbulent-like flow with no distinct frequency bands. The current study provides a plausible mechanistic explanation for the high-frequency sounds observed in cerebral aneurysms, and suggests that narrow-band (vortex-shedding type) flow might stimulate the wall more, or at least at lower flow rates, than broad-band, turbulent-like flow.

Supplemental Peak Filters for Advanced Disturbance Rejection on a High Precision Endeffector for Robot-Based Inline Metrology

This article presents a metrology platform (MP) as high precision endeffector of a robot with a tailored disturbance rejection scheme in order to enable high-resolution measurements directly in a production line. The MP is installed on a gantry robot for in-plane positioning and has an electromagnetic actuator for vertically positioning its mover. It can mount a compact measurement tool for high precision topography measurements, which are typically sensitive to external vibrations, introducing relative motion between the measurement tool and the sample. To compensate these vibrations, the MP mover vertically tracks the sample by feedback control, maintaining a constant distance between sample and measurement tool. In order to reject broad-band floor vibrations as well as narrow-band vibrations, revealed by the analysis and introduced by the robots servo control, the designed high-bandwidth proportional-integral differential based controller is supplemented by peak filters tailored to the narrow-band vibration components. A method for designing these peak filters depending on the location of the narrow-band disturbance relative to the crossover frequency is presented. The resulting controller enables a tracking error as small as 15 nm (rms), which is 50% smaller than the error without the peak filters, demonstrating the effectiveness of the MP in enabling high-resolution inline measurements.

Experimental study on resonant acoustic damping for cabin noise reduction

Abstract Toward the goal of overcoming the weight-and-space redundancy caused by simple implementations of various noise-reducing structures each with a single function, it is natural one of the effective solutions that combine the forms and performances of different noise-reducing structures subtly. To this end, we ingeniously blend the dynamic absorber and the damping material into one structure, which is denoted as the resonant acoustic damping (RAD). In this letter, we conducted several preliminary experiments on an aircraft cabin model to verify the effectiveness of RAD for vibration suppression and noise reduction on complex engineering structures. The experimental results show that RAD possesses a dual-effect feature, that is, the narrowband vibration absorption like dynamic absorbers and the broadband vibration suppression like damping materials.

Narrow Band Vibration Measurement System With Electrodynamic Transducer Seismograph and Modeling Verification

In this paper, a transducer that measures vibration based on a loudspeaker is described. The mathematical model was derived and simulated by understanding the operating principles of the vibration sensor as a model of an inertial force generator. The experimental setup was carefully designed and the outputs from the ADXL335 accelerometer were used for comparison with the output voltage, Vo of the vibration transducer. The experimental results for Vo are in broad agreement with the accelerometer trends. The ADXL335 accelerometer outputs were also used to validate the vibration transducer model by comparing the vibration transducer output voltage, Vo, with the simulation output voltage, Vso. Both the vibration transducer and simulation outputs obtained peak energy when the weight was set at 171.41 g [gram]. The vibration transducer and approach used to optimize the transducer parameters presented in this paper have the potential to be used as a useful tool for the detection of seismic signals.

Wideband Vibrations Rejection of Tip-Tilt Mirror Using Error-Based Disturbance Observer

Vibration rejection is a key technology of practical engineering, especially in optical telescopes with a stable accuracy of urad level. The closed-loop performance of optical telescopes is largely determined by the control bandwidth, while it is severely limited by the low sampling rate and large time delay of the image sensor, so it is difficult to mitigate structural vibrations in optical telescopes, especially wideband vibrations, because they exist universally and greatly influence the stability of the system. This paper develops an improved error-based disturbance observer (EDOB) based on the Youla parameterization approach to mitigate wideband vibrations in optical telescopes. This novel method can greatly improve the vibration rejection ability of the system by designing a proper Q-filter to accommodate wideband vibrations when their frequencies can be acquired. Because wideband vibrations in optical telescopes can be considered as multiple narrow-band vibrations with similar central frequencies, a novel Q-filter instead of a single wideband notch filter is proposed to mitigate wideband vibrations when considering the stability and closed-loop performance of the system. Moreover, this method only relies on a low frequency model, leading to a reduction in model dependence. Both the simulations and experimental results show that the error-based disturbance observer based on Youla parameterization can greatly improve the closed-loop performance of the system compared with the traditional feedback control loop.

Hysteresis compensation control of a dielectric elastomer vibration isolator

This paper describes the design and fabrication of a dielectric elastomer actuator vibration isolator and accompanying hysteresis compensation controller. The results of experiments to elucidate the hysteresis properties and the quality of the vibration isolation are also presented. The model used to characterize the hysteresis properties of the dielectric elastomer actuator is based on the controlled auto-regressive model and employs the recursive least squares method. A closed-loop proportional–integral–derivative controller was developed to compensate the hysteresis and was tuned via the back propagation neural network algorithm. The results demonstrate that the controller can compensate the hysteresis of the dielectric elastomer actuator, and the dielectric elastomer actuator can be used to isolate incoming vibration from the base. When tested using a narrow band vibration in a 5 Hz band, the isolation of the dielectric elastomer actuator vibration isolator was 45.60% across the frequency band.

IMU-Based Attitude Estimation in the Presence of Narrow-Band Noise

In this paper, we consider the inertial measurement units (IMUs) based attitude estimation, a common core problem in a large variety of robotic systems. In particular, we focus on the case where the IMU measurements are contaminated by narrow-band vibration noises caused by the system flexible mode, aerodynamic turbulence, or rotating parts (e.g., motors). Our proposed scheme is a complete solution to adaptively estimate the narrow-band noise and actively compensate it in the attitude estimation. More specifically, the scheme adopts a notch filter to attenuate the narrow-band noise and subsequently embeds such filter into a multiplicative extended Kalman filter framework to eliminate the induced transient error. Furthermore, a least mean square method is utilized to estimate the dominant noise frequency in real time, forming an adaptive notch filter that can effectively attenuate the narrow-band noise with time-varying dominant frequency. The complete algorithm is verified on an actual gimbal system with exhaustive experiments.

Using an Adaptive Filtration to Improve Adaptive Optical Systems Performance. Analytical Review

For adaptive optical systems (AOS) installed in the optical path of aircraft-based laser systems, the presence of changing input light signals is typical. A wave-front sensor processes these signals. The quality of the radiation wave-front correction depends on how well the rapidly changing input signal is received and processed. When dealing with such signals, an adaptive filtration (AF) is used, which allows automatic adaptation to the changing input signal. The adaptive filtration is used in control algorithms for adaptive optical systems.The paper gives a brief theoretical AF background as applied to the AOS. The AF with feedback can be used for the following: a) predictions, b) identification of an unknown system, c) balancing of characteristics, d) disturbance rejection. The AF main point is to control the weighting factors of the input signal, which form the output signal. Under control, the difference between the reference and output signals is minimized. Mathematically, this comes down to defining the global minimum of the objective function. Among the search methods for this minimum, the paper considers the following ones: the Newton's method, the steepest-descent method and its modified version - the least square error method, and the recursive AF algorithm using the least squares criterion. The choice requirements for an adaptive algorithm are formulated.The paper considers direct application of the AF methods in the control algorithms of the AOS used in the airborne laser systems. Analyzes both the works on improving operation of classical AOS control loops (based on the PID-controllers with time-fixed gains) by adding various adaptive devices to the circuit, and the works on direct use of the adaptive filters and their relevant control algorithms. Adaptive filtering has shown the positive results both in suppressing the multiple narrow-band vibrations inherent in the aircraft and in broadband jitter due to the turbulent atmosphere, including the aero-optical wave-front aberrations of laser radiation.For more successful application of the adaptive filtering methods for AOS control, further interpretation and research into capabilities of their practical implementation for specific applications of adaptive optics is required.

Optical fiber vibration sensing system using delay line method

AbstractA delay line method for a distributed optical fiber vibration sensing system is reported. The sensing system is a combination of non‐balanced Sagnac/Mach‐Zehnder structure and an adjustable optical fiber delay line. The vibration location principle is the expansion of conventional null‐frequencies theory, which needs to adjust the length of delay line, in order to determine a zero point in the amplitude variation curve of detected light intensity for one characteristic frequency appearing in the vibration signal spectrum. Moreover, the location simulation using delay line method for narrowband vibration signals is affected. Finally, the experiment verifies that the location errors of vibration events are within ±70 m. The main advantage of proposed method is that it can locate not only the broadband vibration but also the narrowband vibration.

Broadband Vibration Isolation for Rods and Beams Using Periodic Structure Theory

The alternating stop-band characteristics of periodic structures have been widely used for narrow band vibration control applications. The objective of this work is to extend this idea for broadband excitations. Toward this end, we seek to synthesize a longitudinal and a flexural periodic structure having the largest fraction of the frequencies falling in the attenuation bands of the structure. Such a periodic structure when subjected to broadband excitation has minimal transmission of the response away from the source of excitation. The unit cell of such a periodic structure is constituted of two distinct regions having different inertial and stiffness properties. We derive guidelines for suitable selection of inertial and stiffness properties of the two regions in the unit cell such that the maximal frequency region corresponds to attenuation bands of the periodic structure. It is found that maximal dissimilarity between the neighboring regions of the unit cell leads to maximal attenuating frequencies. In the extreme case, it is found that more than 98% of the frequencies are blocked. For seismic excitations, it is shown that large, finite periodic structures corresponding to the optimal unit cell derived using the infinite periodic structure theory has significant vibration isolation benefits in comparison to a homogeneous structure or an arbitrarily chosen periodic structure.

Research on Control Technologies for a High-Precision Multi-Source Vibration Simulation System

Vehicles commonly suffer from the narrow-band noises and vibrations, usually a superposition of multiple sinusoidal signals, due to the excitations of engines, electrical motors, gear boxes, and other rotating mechanical parts. These excitations are transmitted to a reference point of some structure with certain transmission paths. The vibration signal measured at the reference point can be used for power system monitoring, fault diagnosis, modal analysis, noise analysis, etc. For convenience, researchers in a laboratory usually use shakers to generate expected narrow-band vibration signals acting on the vehicle structure reference points to simulate the vibration signals. However, there is a prominent difficulty in ensuring the amplitude and phase accuracy of each sub-frequency component simultaneously. In order to improve the accuracy of generating the expected vibration signal, this paper presents a multi-source vibration simulation control technology based on the tracking filter method. The main idea is to use the tracking filter to estimate the amplitude and phase of the target sub-frequency component accurately. Further, on the target sub-frequency, the drive signal of shakers is then corrected based on the amplitude and phase errors to achieve a more accurate target vibration signal. The amplitude and phase of each sub-frequency component in the excitation signal can be controlled independently. Compared with other Fast Fourier Transform (FFT)-based frequency domain analysis algorithms and numerical methods by solving the equations, the tracking filter method has a higher frequency resolution and higher accuracy. It can be easily realized in real time applications due to its simplicity. Finally, verification experiments are completed. The experimental results show that the multi-source vibration simulation control technology presented in this paper can achieve high-precision amplitude and phase on each sub-frequency component of the target vibration signals, which contain up to eight sub-frequency components.

Youla–Kucera Parameterization-Based Optimally Closed-Loop Control for Tip–Tilt Compensation

In this paper, we develop a new method based on Youla–Kucera parameterization in frequency domain to reduce tip and tilt vibrations of astronomical telescopes. This proposed method can be implemented in real time and can also achieve optimal correction when frequencies of vibrations are provided. Based on this parameterization, the closed-loop stability is easily assured, which can relax the stability condition to design control parameters. Due to being plugged into an existing feedback control loop, the sensitivity function of the tip–tilt mirror control system can be minimized by optimizing Q-filter for adapting the changes of vibrations. Two types of Q-filter are introduced to deal with low-frequency and large-magnitude narrowband vibrations. Because of not being restricted by an accurate model of tip–tilt mirror, this improved control mode cannot lead to a compromise between vibrations rejection and noise propagation in the control loop. Although on-line identification of disturbances models is not required, finding the vibration frequencies is crucial. Simulations and experiments demonstrate that the Youla–Kucera controller has a clear improvement of the closed-loop performance in comparison with the original method.

Effects of Stochastic Excitation and Phase Lag of Pedestrians on Lateral Vibration of Footbridges

Incidents of pedestrian-induced large lateral vibrations of footbridges reveal the occurrence of an instability-type phenomenon in pedestrian-induced vibration. However, the mechanism involved has yet to be clearly explained. In this work, a novel model for predicting the lateral vibration of footbridges is proposed. Under an algebraic framework of nonlinear stochastic vibration, the narrow-band vibration caused by the pedestrian intra-subject randomness and the phase lag between the footbridge motion and the pedestrian load are considered. The critical condition that triggers the large lateral vibration of the footbridge is identified using the stochastic averaging method and the concept of stability based on the Lyapunov exponent. The validity of the proposed method is confirmed through case studies of three bridges. Through a parametric analysis, the effects of several crucial parameters on the stability/instability of vibration are discussed. Finally, conclusions are drawn regarding insights that can be useful to the future designs of footbridges.

Selective model inversion and adaptive disturbance observer for time-varying vibration rejection on an active-suspension benchmark

This paper presents an adaptive control scheme for identifying and rejecting unknown and/or time-varying narrow-band vibrations. We discuss an idea of safely and adaptively inverting a (possibly non-minimum phase) plant dynamics at selected frequency regions, so that structured disturbances (especially vibrations) can be estimated and canceled from the control perspective. By taking advantage of the disturbance model in the design of special infinite-impulse-response (IIR) filters, we can reduce the adaptation to identify the minimum amount of parameters, achieve accurate parameter estimation under noisy environments, and flexibly reject the narrow-band disturbances with clear tuning intuitions. Evaluation of the algorithm is performed via simulation and experiments on an active-suspension benchmark.

Distributed lock-in drives broadband vortex-induced vibrations of a long flexible cylinder in shear flow

AbstractA slender flexible body immersed in sheared cross-flow may exhibit vortex-induced vibrations (VIVs) involving a wide range of excited frequencies and structural wavenumbers. The mechanisms of broadband VIVs of a cylindrical tensioned beam of length-to-diameter aspect ratio 200 placed in shear flow, with an exponentially varying profile along the span, are investigated by means of direct numerical simulation. The Reynolds number is equal to 330 based on the maximum velocity, for comparison with previous work on narrowband vibrations in linear shear flow. The flow is found to excite the structure at a number of different locations under a condition of wake–body synchronization, or lock-in. Broadband responses are associated with a distributed occurrence of the lock-in condition along the span, as opposed to the localized lock-in regions limited to the high inflow velocity zone, reported for narrowband vibrations in sheared current. Despite the instantaneously multi-frequency nature of broadband responses, the lock-in phenomenon remains a locally mono-frequency event, since the vortex formation is generally synchronized with a single vibration frequency at a given location. The spanwise distribution of the excitation zones induces travelling structural waves moving in both directions; this contrasts with the narrowband case where the direction of propagation toward decreasing inflow velocity is preferred. A generalization of the mechanism of phase-locking between the in-line and cross-flow responses is proposed for broadband VIVs under the lock-in condition. A spanwise drift of the in-line/cross-flow phase difference is identified for the high-wavenumber vibration components; this drift is related to the strong travelling wave character of the corresponding structural waves.

Multi-frequency vortex-induced vibrations of a long tensioned beam in linear and exponential shear flows

The multi-frequency vortex-induced vibrations of a cylindrical tensioned beam of aspect ratio 200, free to move in the in-line and cross-flow directions within first a linearly and then an exponentially sheared current are investigated by means of direct numerical simulation, at a Reynolds number equal to 330. The shape of the inflow profile impacts the spectral content of the mixed standing-traveling wave structural responses: narrowband vibrations are excited within the lock-in area, which is limited to a single region lying in the high flow velocity zone, for the linear shear case; in contrast, the lock-in condition occurs at several spanwise locations in the exponential shear case, resulting in broadband responses, containing a wide range of excited frequencies and spatial wavenumbers. The broadband in-line and cross-flow vibrations occurring for the exponential shear current have a phase difference that lies within a specific range along the entire span; this differs from the phase drift noted for narrowband responses in linear shear flow. Lower vibration amplitudes, time-averaged and fluctuating in-line force coefficients are observed for the exponential shear current. The cross-flow force coefficient has comparable magnitude for both inflow profiles along the span, except in zones where the broadband vibrations are under the lock-in condition but not the narrowband ones. As in the narrowband case, the fluid forces associated with the broadband responses are dominated by high frequencies related to high-wavenumber vibration components. Considerable variability of the effective added mass coefficients along the span is noted in both cases.

Research on mechanism of the large-amplitude and narrow-band vibration of a flexible flat plate in the rectangular channel

Further experiments and theoretical analysis were performed to investigate mechanism of the large-amplitude and narrow-band vibration behavior of a flexible flat plate in a rectangular channel. Test plates with different thicknesses were adopted in the FIV experiments. The natural vibration characteristics of the flexible flat plates in air were tested, and the added mass theory of column was used to analyze the flexible flat plates’ natural vibration characteristics in static water. It was found that the natural vibration frequency of a certain test plate in static water is approximately within the main vibration frequency band of the plate when it was induced to vibrate with the large-amplitude and narrow-band in the rectangular channel. It can be concluded that the harmonic between the flowing fluid and the vibrating plate is one of the key reasons to induce the large-amplitude and narrow-band vibration phenomenon. The occurring condition of the phenomenon and some important narrow-band vibration characteristics of a foursquare fix-supported flexible flat plate were investigated.

A Minimum Parameter Adaptive Approach for Rejecting Multiple Narrow-Band Disturbances With Application to Hard Disk Drives

Many servo systems are subjected to narrow-band disturbances that generate vibrations at multiple frequencies. One example is the track-following control in a hard disk drive (HDD) system, where the airflow-excited disk and actuator vibrations introduce strong and uncertain spectral peaks to the position error signal. Such narrow-band vibrations differ in each product and can appear at frequencies above the bandwidth of the control system. We present a feedback control scheme that adaptively enhances the servo performance at multiple unknown frequencies, while maintaining the baseline servo loop shape. A minimum parameter model of the disturbance is first introduced, followed by the construction of a novel adaptive multiple narrow-band disturbance observer for selective disturbance cancellation. Evaluation of the proposed algorithm is performed on a simulated HDD benchmark problem.

Large-amplitude and narrow-band vibration phenomenon of a foursquare fix-supported flexible plate in a rigid narrow channel

An experiment was performed to analyze the flow-induced vibration behavior of a foursquare fix-supported flexible plate exposed to the axial flow within a rigid narrow channel. The large-amplitude and narrow-band vibration phenomenon was observed in the experiment when the flow velocity varied with the range of 0–5 m/s. The occurring condition and some characteristics of the large-amplitude and narrow-band vibrations were investigated.

Fabrication and characterization of a wideband MEMS energy harvester utilizing nonlinear springs

This paper presents the fabrication, characterization and modeling of a wideband MEMS electrostatic energy harvester utilizing nonlinear springs. The experimental results show that the vibration energy harvester displays a strong softening spring effect. For narrow band vibration, the energy harvester exhibits a widening bandwidth during frequency down-sweeps. For increasing levels of broadband random noise vibration, the energy harvester displays a broadening bandwidth response. Furthermore, the vibration energy harvester with softening springs not only increases the bandwidth, but also harvests more output power than a linear energy harvester at a sufficient level of broadband random vibration. At a broadband random vibration of 7.0 × 10−4 g2 Hz−1, we found that the bandwidth increases by more than 13 times and the average harvesting output power increases by 68% compared to that of a linear vibration energy harvester. Numerical analysis confirmed that the softening springs are responsible for the band broadening.